Inhalation exposure to cigarette smoke promotes neointimal formation in mouse model of arterial injury

Smoking is a well-established risk factor for cardiovascular diseases, yet direct evidence linking cigarette smoke (CS) exposure to neointimal formation remains limited. To address this gap, we investigated the effects of CS exposure on neointimal formation using an injury-induced arterial mouse model. Neointimal formation was induced in the femoral artery via mechanical injury with a guidewire, and mice were exposed to CS generated from 3R4F reference cigarettes at a total particulate matter concentration of 600 µg/L for 2 h daily. CS exposure commenced three days prior to injury induction and continued until euthanasia on days 7 or 14 post-injury. CS exposure significantly exacerbated neointimal formation; however, in the absence of injury, it did not induce structural alterations in the femoral artery. In vitro, cigarette smoke extract (CSE) at 0.1%-corresponding to approximately 50 ng/mL nicotine, a clinically relevant concentration in smokers-enhanced the proliferation of aortic smooth muscle cells, a critical process in neointimal development. However, CSE exhibited minimal effects on other cellular processes involved in neointimal formation, including phenotype switching, adhesion, migration, and extracellular matrix deposition. Mechanistically, CSE exposure increased Akt and FOXO3a phosphorylation, leading to a downregulation of p27 and an upregulation of CDK2 and cyclin E, ultimately promoting Rb phosphorylation and cell cycle progression. In conclusion, although CS alone does not appear sufficient to initiate neointimal formation, it significantly exacerbates or accelerates its progression in a primed vascular environment. The promotion of vascular smooth muscle cell proliferation via cell cycle progression may underlie this effect.